Electrical musical device



June 27, 1950 A. ROTH ELECTRICAL MUSICAL DEVICE 2 Sheets-Sheet 1 Filed Oct 22, 1947 I N V EN TOR. ,a/s /Vpw E075 Patented June 27, 1950 UNITED STATES PATENT OFFICE ELECTRICAL MUSICAL DEVICE Alexander Roth, Bronx, N. Y.

Application October 22, 1947, Serial No. 781,469

8 Claims. 1

My present invention relates to a system for electronically producing musical notes, said notes being controlled by a keyboard similar to a piano keyboard, whereby a photoelectric system consisting of beams from a plurality of light sources controlled by an electrical keying circuit, revolving perforated discs which periodically interrupt the beams, photoelectric cells which transform the interrupted light beams to electrical impulses fed into an amplifying apparatus, and loudspeakers to create the sound, are used to produce musical notes of a complex waveform which consist of a fundamental frequency combined with any desirable number of its upper harmonics.

It is a further object of my invention to provide the means for an electrical sustaining pedal analogous to the damper pedal of a conventional piano, which will allow any number of notes to continue to sound with diminishing or damped intensity for a period of time after the keys corresponding to these notes have been struck and then released, while the sustaining pedal is held depressed, for the purpose of achieving improved and more interesting tonal effects and permitting the performance of musical passages not possible with two hands in previous photo-electric musical instruments without a sustaining pedal.

It is a further object of my invention to provide an electrical circuit which will permit the operator to regulate the intensity envelopes of the musical notes. At the will of the performer, these notes may be of a staccato or quick attack nature which means that the note reaches its average intensity value instantly when the key is depressed, and when thekey is released, it ceases immediately, an effect common to certain woodwinds and strings. Notes may also be produced of a diminishing or damped nature Where the notes reach their average value or their zero value by gradual degrees making for a soft effect, common to pipe organs and mellow brass. The notes may also be made to have a percussive nature in which case the note begins with an initial percussive pulse similar to the type of note produced by a piano or a guitar, or of any instrument in which the notes are produced by tapping or plucking strings. The notes may also be made to diminish to zero intensity while the key is held down, or to sustain themselves without loss in volume for the entire duration of key depression. In general, an intensity envelope consisting of different combinations of the above may be combined at the will of the performer, to imitate the intensity qualities of practically any instrument in existence.

It is a further object of my invention to eliminate the excessive costs required in producing electrical musical instruments due to the requirements of the keying system. Most other instruments require that the keys control many sets of contacts, each of which contacts must over a long period of time maintain a negligible resistance across the key terminals. In my keying system it is necessary for each key to control the equivalent of a double pole double throw switch, the contacts of which do not necessarily have to be of expensive metals. Keying noises are also automatically made negligible due to certain characteristics of the circuits as will be described later.

It is a further object of my invention to provide a system for regulating the extent to which any or all of the upper harmonics will be present in the musical notes, thus making it possible to regulate the musical quality of timbre of the entire instrument to make possible the creation of similar tonal qualities to most other instruments, also to create original tonal effects of instruments not yet produced or in existence.

A further object is to provide a simple vibrato producing device. By a vibrato I mean a conventional type vibrato, or one which consists of periodic frequency fluctuations. The period of fluctuation to be used is a frequency of about '7 V. P. S., as this is a pleasing frequency for a satisfactory vibrato. In my instrument, it is not only possible to produce the vibrato, but it is also possible to vary the frequency range thru which the frequency fluctuations occur. To illustrate the vibrato control possible with the use of the vibrato mechanism, assume that note A having a frequency of 220 C. P. S. is sounding. It is possible to vary A from 219.5 to 221.5 C. P. S., or between'218 and 222, or any desired range with seven variations each second in every case. This novel vibrato control permits the operator to vary the intensity of the vibrato effect to suit the particular musical composition being played, or to more closely imitate the different vibrato qualities of the other instruments.

It is a further object of my invention to provide a pedal control which makes it possible to obtain any desired intensity level instantly by means of one foot operating one of two pedals, which makes louder or softer any previous average setting of the volume control.

It is a further object of my invention to provide a photoelectric signal generator which is compact enough to make the overall size of the instrument about one third the size of a spinet style piano, and many times lighter. By making the pedal'support and the legs removable, the

instrument may be light and small enough to be considered portable.

In general, the main object of my invention is to provide a compact musical solo instrument which has a piano type keyboard and is played like a piano. This instrument has a sustaining pedal similar to that of a conventional piano, but also has volume control pedals. This instrument makes possible complete control of all of the characteristics which musical notes have, making possible the imitation of any musical instrument. It is possible to control the tonal intensity envelopes to produce tones with any degree of shading from full percussion to very soft, with a sustaining or decaying nature having any desirable conventional tone ending. It is possible to completely control the harmonic content of the notes by sounding any desirable number of upper harmonics along with the fundamental making possible tonal qualities nearly identical with the tones of any other musical instrument, or of tones never before used. It is also possible to make tonal imitation complete, to control the vibrato effects so that the wide-vibrato of the violin, or the barely perceptible vibrato of the piano may be copied and included in the tonal characteristics.

I do not wish to limit the invention specifically to the construction, the wiring diagrams, and the circuit constants as presented, as these may be altered without departing from the scope of the original invention, by those skilled in the various arts, to vary according to the adaptation.

To more completely illustrate my invention, and to bring out its advantageous possibilities, reference will be had to the accompanying drawings, in which:

Fig. 1 shows a perspective view of a form which my invention may take.

Fig. 2 shows the electrical circuit of the two volume pedals.

Fig. 3 is a circuit diagramof part of the keyboard to illustrate the bulb circuits and the harmonic circuits.

Fig. 4 is a diagrammatic representation showing the photoelectric cell, the amplifying system and the vibrato-tremolo device.

Fig. 5 shows graphically the output wave shape of the vibrato oscillator.

Fig. 6 shows a method for simultaneously varying a number of variable resistors.

Fig. 7a shows a plan view of the signal generating unit.

Fig. 7b shows a front view of the signal generating unit.

Fig, 8 is a fragmentary enlarged view of the signal generator, showing the scanner disc and light sources.

Fig. 9 shows the circuit diagram for controlling the intensity envelopes.

1 Figs. a, 101), and 100 show graphically several intensity envelopes possible with the circuit of Fig. 9.

A form of my invention is illustrated in Fig. 1 which shows the various controls, and the decrease in size possible over most other types of keyboard instruments. It is understood, however, that the exact size and shape of this cabinet shown is by way of example only. The pedals are shown at I, 2 and 3. The sustaining pedal is at I, while 2 is the pedal whichwill decrease the sound level to zero, and pedal 3 will increase the sound level to its maximum intensity. Variable panel controls are shown at 4 and 5. The operation of the controls at 4 and will be described in detail later. There is a loud speaker baflie, and a treble speaker, of the instrument, not shown. These speakers are connected to the outputs of two power amplifiers, respectively, a bass and a treble booster amplifier. This is done to insure richer tone in the bass and treble, and to simulate the production of the higher notes on the right side, and the lower notes on the left side, as in a conventional piano. A combination fluorescent lamp and music rest is shown at l. the lamp being operable from the usual power supply line which energizes the instrument.

The dotted oblong shown at 8 represents the approximate dimensions of an enclosure for all the electronic and mechanical equipment needed for the instrument and not used directly at the keyboard, or on the panel. This box, which may be made removable for repairs, may conveniently be put therefore, in the position shown at 8 just behind the keyboard and the panel. One half of the container, which may represent the chassis upon which the electronic apparatus is mounted, is seen to be of sufficient volume to hold the following, which will be a complete listing of all the electronic apparatus necessary: Two 300 volt D. C. supplies, one preamplifier and its supply, one bass power amplifier and its supply, one treble power amplifier and its supply, a vibrato oscillator and its supply. The other half of the box contains the signal generating unit. The dimensions of the complete container 8 may be assmall as approximately four feet long, sixteen inches in height, and about one foot deep. This gives about two and one half cubic feet to each half of the box which is sufiicient for the electronic equipment needed, and for the signal generating unit. This instrument has 85 keys in the keyboard 9, or the keyboard extends for exactly 7 octaves, or in the system of notation to be used, from C1 to Ca.

Figure 2 shows a suggestion for the connection of the volume pedals. A view is shown between two stages of the voltage amplifier section. When pedals l0 and H are undepressed, any desired level of volume may be obtained by the setting of the panel volume control potentiometer l2. If resistor of pedal H) has a value of about 1,000,000 ohms, then by depressing pedal [0, the intensity level may be gradually increased to approximately the maximum value. Similarly, by depressing pedal ii, the sound level can be made to vary from its setting on potentiometer 82, gradually down to zero. This pedal arrangement makes full and continual volume control possible with one foot. The potentiometer I2 is one of the controls on the panel of the instrument.

Fig. 3 will now be considered. Fig. 3 shows the wiring circuit for part of the keyboard including the system used for regulating the harmonic content of the sounds. With the wiring system of Fig. 3, it is possible to produce musical notes which comprise a fundamental, and to any predetermined extent or intensity, the presence of any other note of 2, 3, 4, 5, 6, or n times the frequency of the fundamental note. The second multiple will be called the 2nd harmonic, the third multiple will be called the 3rd harmonic, etc. By the proper synthesis of the fundamental with appropriate harmonics with theirappropriate intensities, it is possible to recreate the sound quality of any musical instrument, also sounds of instruments not yet produced. With my present invention, it is possible to do just that, but for simplicity of ex- Fig. .4 represents, in a box diagram, the photoelectric cell which translates the interrupted light beams, from bulbs l6 of Fig. 3, to electrical energy, the amplifying system, and the means for a vibrato device.

In Fig. 4 the perforated revolving disc is shown cross-sectionally at 29, interrupting beams of light 39, from bulbs l6, which eventually hit photoelectric cell 3!. The impulses from the photoelectric cell are fed into amplifier 32 and into two separate final power stages 33 where the bass and the treble are boosted individually. This separate bass and treble are then conducted to two independent speakers 34. The volume pedals previously described are shown symbolically at 35. 35 and 37 represent volume and tone controls respectively, the vibrato oscillator is shown at 38.

The vibrato oscillator may be any type of electrical oscillator, which generates a frequency of about 7 C. P. S., which is approximately the best vibrato frequency. Part of this output is fed into field coils 39 of horseshoe type magnet 40. The output into the coil is the superimposition of the oscillators sinusoidal output upon a steady and invariable D. C. voltage. This is accomplished by a D. C. supply 4i, in series with potentiometer 42 and coil 39. The amplitude of the sinusoidal portion is controlled by potentiometer 42. In this way a number of voltage curves as shown in Fig. may be obtained, where V1 represents the value of the invariable D. C. portion. 43 represents a thin metallic disc attached to the shaft of the driving motor. (Actually it is indirectly attached to the shaft thru a gear train, but this makes no difference in explaining the principle.) If any current is allowed to flow thru the magnet field coil 39, then the magnetic lines of force between the poles of magnet 49 will induce eddy currents into the metallic disc 43 while it rotates. These currents will then set up a counter-torque which is constantly proportional to the current thru the magnets field coil 39, if the iron in the magnet is not saturated. Thus, if the voltage output from the vibrato oscillator of Fig. 5 is passed thru the field coil 39, there will be a, constant unvarying torque due to the constant current of the biasing D. C. voltage V1, and there will also be a resultant increase and decrease in torque due to the action of the varying portion of the curve. The motor will thus gain and lose speed with a regular period equal to the frequency of the vibrato oscillator, or about '7 C. P. S. The amplitude of variation, or the width of the speed shift of the motor may be controlled by potentiometer 42 which determines the amplitude of the sinusoidal portion of the curve. As the motor changes its speed periodically, the rotating disc light choppers 29 are caused to experience this same speed variation. Thus, the frequency with which any beam of light 30 is interrupted varies regularly with time, and a pleasing vibrato will be heard. The range or width of the frequency shift of each note as a result of the vibrato is seen to be also governed by potentiometer 42, which controls the variable portion of the vibrato oscillators output. In Fig. 5, it is also possible to express the width of the maximum frequency shift in a percentage of the steady frequency of the note, where the natural or steady frequency is considered to be 100%. When the curves of Fig. 5 are above the bias line indicated by V1 the frequency of the note will be less than 100% and when it is below, it is more than 100%. The percentage frequency shift depends on the width of the variable portion, and this percentage, it should be noted, is the same for all of the notes of the entire keyboard, so that the vibrato will not be more obvious in notes of particular sections of the keyboard.

In Fig. 6 is shown a suggestion for a method of varying a multiplicity of resistors all at the same time and with only one movement. A number of slider arms 44 are placed on the same driving axle 45, and are pressed against resistor element 46 so that when the :axle 45 is rotated, all of the slider arms 44 are moved to the same corresponding position along the resistance element. Since as many as of these potentiometers may be needed back to back, they might make a unit which is too long to be placed into the instrument, it is suggested that the unit be made in two parts, one part 47 driven directly from the axle 45, the other part 41 driven from gear 48 on axle 45 and gear 49 connected to the axle 45 of the other section 41'. This is the suggested system to be used with potentiometers 18 of Fig. 9, and all the harmonic resistors l8, l9 and 20, etc., of Fig. 3. The ones being used for the harmonic resistors, should have a portion of the resistance element 46 lacking, so that for a certain position of the slider arm 44, it should be possible to open the circuit between the contacts of any of the potentiometer banks. The controlling knob located on the panel, is shown at 50.

The signal generating unit will now be con sidered. In Fig. 7a and Fig 7b are shown a top and front view respectively of the unit. 5| represents a rectangular metal frame used to house" the unit. Its rectangular dimensions may be as small as 20 inches long and 12 inches deep. Built into the frame are two shelves 52 which are used to separate the unit into three parts, and to support the various sections. In each of these units is a revolving perforated disc 53, 53", and 53". These discs are driven thru a gear drive as shown, from motor 54. Gear 55 drives gear 55 which turns disc 53". This in turn drives ears 51 and 58 which turn discs 53 and 53 respectively. These gears are of such size that disc 53" turns fastest, 53" turns at /8 the speed of 53", and 53' turns at the speed of 53". The exact speeds of the discs will be discussed later. A side view of the source of light and photocell units are shown at 59 and Bil respectively. 59 represents a cross-sectional view along line '5I6i of Fig. '71) showing one row of the two rows of neon bulb compartments in each three units. The light from these bulbs shines down thru slits 6'! directly beneath them, thru the disc 53, then thru identically positioned slits in the photocell unit 60 directly above the photo-- cells. The purpose of this is to prevent the light from straying from one source thru a set of openings in the disc not corresponding to that source and entering the photocell, sounding notes other than the intended ones. t is also to prevent stray light from entering the photocell. Photo-I cell unit 5|] consists of a photosensitive element placed beneath the slits, the area. of which element is sufliciently large to catch all of the light coming thru all of the slits in the unit. This photosensitive element may be of a standard photoelectric cell of the vacuum or gas filled type, of sufficient working area to receive all the lightv entering unit 69, when properly positioned withinv 5, planation, and-diagramm-in'g, Fig. 3 is shown with onlythe fundamental and the 2nd, 3rd, and 4th harmonic circuits. It must be remembered however, that any number, n, harmonics are possible using the same wiring system, and the novelty'o'f this inventionis not limited to the fourth harmonic.

In Fig. 3, the groups of switches and contacts 13, I4 and I5 represent oneof a set of contacts one of which is closed eyery timeone :key of the instrument is depressed. Assume key l3, or C4 to be depressed. Then a complete circuit will be formed thru bulb Ci of bulbs 16, supply I! and key 13. A complete circuit will also be formed thru key 13, supply i], the .bulb 16 corresponding to the 2nd harmonic of C4 or 1G5, and thru variable resistor 18 .thus lighting. the bulb 16 which represents Cs. similarly the third harmonic of C4, or G5 will light thru variable resistor 19,. and

the 4th harmonic, or 'CL .will light thru variable resistor .20. It is seen that by controlling variable resistors I8, is or .20, any harmonic may be sounded along with the fundamental, with any desired intensity, or by setting any of the resistors into the open position, that harmonic, or partial will be excluded frornthe tone. The corresponding circuit .is also given for the next higher note, '4. It isthus seen that the same bulb may be usedas a fundamental, and as the upper harmonics for other notes, keeping the total-number of bulbs in the construction down to the total number of notes the instrument, or 85. It is also seen that the number of harmonic resistors may run into the hundreds. To overcome the difliculty of regulating so many, I will introduce later, a system whichpermits the regulation of a number of variable resistors at once. By this system, it will be possible to simultaneously vary all the resistors on a horizontal with resistor [8, so that with one movement it will be possible to set them all to the same value.

It is seen by examining the diagram, that all the resistors horizontal to resistor is control the 2nd harmonics of their corresponding notes, as was shown to be the case with C4 and C5. Thus by varying to the same extent all the resistors horizontal to Hi, all the 2nd harmonics ofall the notes will be sounded with the same importance, which is what is wanted. Similarly, all the third harmonics will be regulated by resistors horizontal to I9, and 4th harmonics will be regulated by the resistors horizontal to resistor 20. The lettered horizontal wires 2'! coming from all the fundamental wires 22, indicate that these wires have come from harmonic resistors of the key represented by the letter. Similarly, the letters alongside the 2nd, 3rd and 4th harmonic resistors l8, f9, 20, etc., indicate that these resisters are connected to the bulb indicated by that letter. Using this system, it is possible therefore, 'to wire the instrument to any, nth harmonic, following the previously outlined method.

However, as the circuit now stands, it is possible for current to trace the two following paths, assuming key ['5 to be depressed; (1) Leave supply l'lpgo thru key l5, thru 'firs't harmonic resistor 23 to point 24, then back thru resistor 20 to line "25, from where it may now go thru bulb H3 corresponding to C4, or any of C4S harmonics.

(2-) Leave supply ll and again get to point 24,

down line 26 and thru any of Css harmonic resistors lighting any of (36's harmonics as well as those of key 15 (C). In the two particular cases diagrammed, these two other paths which the current may take do not result in lighting bulbs 6 which are too harmonically injurious to the original note struck, but as is seen from the diagram, this is not always the case. It is possible to light a whole series of bulbs from one key, none of which have any harmonic relation to the original note. To eliminate this difliculty I use several low current crystal rectifiers placed at points 21 and 28. When these rectifiers pass current (current as considered in the conventional direction, flowing from .plus to minus) only in the direction of their arrowheads, then with the polarity of supply I! as indicated in Fig. 3, the faulty current paths described above cannot take place.

The value of D. C. power supply I! is approximately 300 volts, and it should be capable of delivering 150 ma. The bulbs it are of the miniature watt neon variety. The advantage of using high voltages and low current neon bulbs will become apparent later in the transient current effects possible with reasonably sized con-1 densers, to produce various desirable intensity envelopes. The individual bulb circuits are not completely shown, but as will be seen later, there is resistance in the fundamental lines 22 to limit the bulb current. .With the values of those resistances to be described later, the best value of the harmonic resistors I8, I9 and 20 to provide an ample degree of control, is from about 10,000 to 2,000,000 ohms, with an open circuit when the resistors slider arm is rotated thru a large enough angle. The rectifiers 2'1 and 28 are each essentially low current crystal types, which may have a resistance of even hundreds of ohms in the conducive direction, so that needless expense need not be required for obtaining high performance rectifiers.

It is to be noted that not all the notes of the keyboard have all their upper harmonics. Those in the upper ranges may not have some or all of them because the bulbs corresponding to the harmonies of these notes do not exist in the signal generator unit, as only bulbs are used. If the harmonics to these notes were absolutely necessary, the signal generator as described later could be constructed to contain the bulbs corresponding to the upper harmonicsof the higher register notes. But notesin the upper ranges often have harmonics which are not in the audible range, and when they are in the audible range, the notes are of such high pitch to begin with, that the ear cannot easily discern between the fundamental alone, and the fundamental with its'audible harmonies. For this reason, in this '85 key instrument, which is also an 85 bulb instrument, the following table will give the number :of resistors in the groups of the Various harmonic levels. The table is given to the 6th harmonic, as this is generally a desirable and practical highest partial required to permit sumcient tonal flexibility to insure satisfactory results in imitating the tonal qualities of most other instruments.

Table 1 Number of The keys that Harmonic level gt i the resistorsare group connected to 73 I 01 to c. '66 C1 to Fu 61 C1 to Ca 57 O1 to G5# 54. O to F5 the unit. Each rotating disc contains several concentric paths or rows of openings, and there is one bulb of units 59 directly opposite each row of impressions. 62 represents the eddy current disc described previously, and it is shown being driven from the motor gear 55 by gear 63. 64 is the vibrato magnet also described previously.

Fig. 72) represents a front View of Fig. 7a taken along line 55-455 and looking toward the back and front view of one of the light source units 59 is shown in this view. The significance of the numerals in Fig. 7b becomes clear when considered in connection with the explanations of Fig. 7a and Fig. 8.

Fig. 8 shows a bottom view of the light source unit shown at 58 of Fig. 7a. The unit is broken up into two nearly equal rows of compartments 66 each of which houses one bulb it which shines thru its corresponding slit 61. One of the wires from each of the bulbs are brought together as at 68. The other wires are connected commonly to the housing as at 63, then this goes to one of the terminals of the power supply I! described before. The reason for two rows of bulbs, is that each of these bulbs are about A; inch in diameter, and good results are possible with bulbs and rows about 6 to the inch. This would make disc 53' and 53", which hold two octaves, about only ten inches in diameter, and disc 53", which holds a Whole tone less than three octaves, about 14 inches in diameter. A closeup of the pattern on one of the scanner discs is shown at Hi. This pattern which interrupts the light beams, may consist of narrow radial slits. It may also be of such nature that the transparency varies sinusoidally while going from point to point around the path. Actually any impression which will periodically interrupt the light beam may be used, but the previously mentioned ones are easiest to produce and reproduce.

All of the three photocell units 60 are connested in parallel and then connected to the input of the amplifier 32. The entire signal unit of Figs. 7a and 7b fits into the dotted oblong 8 of Fig. 1. If the signal unit is placed with the discs in the vertical plane, and the longest dimension of the rectangle placed parallel to the longest dimension of the oblong 3, then the unit will fit nicely into the right half of the box 8, the left half being reserved for the electronic apparatus.

The motor t d should be of the constant speed synchronous type to avoid fluctuations in speed due to line voltage variations. However these motors exhibit slight speed changes with changing loads, yet return to their original speeds when the loads become constant. This means that the constant bias torque described before will have practically no effect on the motors steady-state speed, but the changing torques due to the sinusoidal tremolo output will produce slight speed fluctuations, no matter how small the sinusoidal portion is compared with the larger bias portion.

The scanner disc may be made of some transparent medium such as glass, in which case copies may be made by photographic means. In this way it may be possible to make large numbers of discs with little trouble in much the same way that many photographs may be made from the negative.

The disc and motor speeds, and the patterns will now be discussed. As will be remembered, the individual tones are generated by light passing thru rows 01"" openings in the revolving discs, resulting in a periodically chopped. beam received and Gm is the diameter of motor gear 55.

by a photocell and amplified. This is a pure tone, and several of these pure tones are combined together in various intensities to produce a complex tone. In the discs, are several rows of openings, each row of which contains a number of openings or cycles. The frequency of any pure tone corresponding to a certain path, is equal to the number of cycles per path multiplied by the speed of rotation. It is seen that a whole number of cycles must exist per path, that is to say that a path cannot contain 32.7 cycles, as the constant phase shift at the end of every rotation would prove to be very annoying. It is therefore necessary to select the frequencies of the pure tones so that with a particular angular velocity, it will be possible to use rows of impressions all of which contain numbers of whole cycles.

The frequencies of the scale I suggest are those listed in Table 2 under frequencies. Discrepancies of one part in three hundred are supposed to be impossible to detect by practically any musician. The frequencies listed comprise a scale in which discrepancies exist only to approximately one part in six hundred when judged with an equal tempered musical scale.

Discs 53' and 53 each have 25 paths and disc 53" has paths making 85 paths in all. In Table 2 the paths are numbered from 1 to 25 and from 1 to 35 going from the inside out. The particular note corresponding to that path is given, and the number of cycles per path is given in the next column. The last column, the note frequency, represents a product between the number of cycles per path, and the speed of revolution. The gear ratio between 53 and 53" is four to one with the gear of 53' being the larger, the gear ratio between 53" and 53" is eight to one with the gear of 53" the larger. The required speed of 53" is .4 R. P. S. To obtain this speed the motors speed would have to be Gd I G'm.

where Gd is the diameter of gear 56 of disc 58", It should be noticed that in the table as presented, note A has concert pitch of 440 C. P. S. Should any other scale with another value of A be desired, it may be produced by forming a simple arithmetic ratio between A-MO and any other A, then adjusting the motor speed proportionally.

In using the values of Table 2, the minimum distance between any two cycles in the same path on the disc will be about of an inch. This distance is not too small as to make construction of the discs unfeasible considering that copies may be photographically made. It should also be noted, that if the radial slit pattern be used, there is no limitation on the exact width of the slits. However, since the spacing of the slits is not exactly the same in all of the paths, the width of the slits should in all of the paths, be proportional to the spacing in that particular row.

In some. musical instruments, it is necessary to make allowances for the intensity distribution over the audible spectrum. This may he done in this instrument by using varying widths of slits, or varying the transparency of the discs over the spectrum to make allowance for the varying intensity of the notes. I prefer not to do this, but to depend on the tone control and the bass and treble booster amplifiers to balance out any intensity differences existing in the-bass and treble portions.

DISC 53.4 R. P. S.

Mention will now be made of the controls of the instrument to show the capabilities of the L. Tone end control.

bulbs.

instrument. If the instrument is wired for the 6th harmonic, then there are twelve regulators on the panel 4 and 5 of Fig. 1, two switches, and three pedals. A brief description of the controls is as follows:

Switches A. To turn the entire instrument on and oif. B. To turn the fioure'scent lamp on and oil.

Pedals C. A diminishing intensity pedal. D. An increasing intensity pedal. E. A sustaining pedal.

Panel regulators F. A volume regulator. (Continuous control from zero to maximum intensity.)

G. A tone regulator. (Continuous control from I bass to treble.)

H. Vibrato control. (Continuous control over amplitude of periodic (7 C. P. S.) frequency fluctuations.)

I. Tone-start control. (Control produces either percussive or diminishing tone-start.)

J. Tone-start control. (Controls continuously eiTect of tone-start set by I, from staccato to full percussion, or staccato to very soft.)

K. Duration-of-tone control. (Produces either sustained tone, gradually damped tone, or rapidly damped tone while the key is held down.)

(Produces either staccato,

soft, or very soft endings to tone when key,

or sustaining pedal is released.)

M, N, O, P, Q. 2nd, 3rd, 4th, 5th and 6th harmonic regulators. (There is no limit on the number of harmonic regulators.)

Thus far, the functioning of all the controls except E, J, K, L and M were discussed. Figures 9 and 10 which illustrate these controls will now be taken up.

Fig. 9 represents a complete schematic circuit of any bulb circuit of Fig. 3. The bulbs described before are shown at It. All the switches controlled by one key are shown to be controlled from key bar H. When the key is undepressed, poles l2 and 13 of the switches touch contacts 14 and 15 respectively, and when key ll is depressed, the poles touch contacts 76 and 11 respectively, both poles always moving as a unit with key 1|.

Fig. 10 represents the variou intensity envelopes of the notes which may be obtained by means of circuit of Fig. 9. Fig. 10a represents curves which show what happens only the instant the key is depressed, 10b shows the intensity envelopes during the time that the key is held depressed, and shows the curves representing what happens the instant the key is released. Any combination of a, b and c may be formed with the circuit of Fig. 9 to produce any desirable note shape.

If key H is depressed, then there will be a complete circuit from the plus terminal of supply Il thru contact 11 and pole i3, potentiometer 18, rectifier 28, bulb l6 and back to the negative terminal of supply ll, lighting bulb l6. There will also be complete circuits thru the harmonic resistors I8, I9 and 20, lighting the harmonic It is this which is the bulb circuit illustrated in Fig. 3.

When the key H is in the undepressed position as shown in the diagram, it i seen that condenser 19 is kept in a discharged state thru circuit would exist across the terminals of condenser 19 resulting in a high initial current, and excessive sparking at the key contacts. The resistor 80, which has as resistance of approximately 300 ohms serves to limit the peak discharge current and prevent excessive sparking. It is necessary that condenser 19 be discharged rapidly upon releasing the key. and the value of resistance 80 which is suggested, will not interfere with. the rapidity required.

It is seen now, that every time key H is depressed, there is an uncharged condenser across a portion of potentiometer 18 determined by the position of slider arm 8!. This uncharged condenser will prevent a rapid buildup of voltage across that portion of the potentiometer which it shunts, the instant that key H is depressed, or at the very beginning of each note. This means that bulb It will have a correspondingly larger voltage across it at the beginning, of each note, until condenser l9 reaches a steady state charge, after which, the bulb intensity will gradually decrease to a value determined by the total resistance of potentiometer T8. The degree of amplitude of the initial pulse in the bulbs intensity every time key H is depressed, will bedetermined by the position of slider arm 8|. When slider arm 3! places condenser I9 across the greatest portion of potentiometer 18, then the pulse will be most exaggerated, and when the condenser is across the least portion, the pulse is least noticeable, with many intermediate values possible.

In Fig. 10 is shown what happens when the key. is depressed. Curve 82 shows the maximum effect possible as just described, and curve 83 shows the minimum effect possible. It should be noticed that these intensity envelopes correspond. to certain musical tone envelopes. The curves between 82 and 83 represent varying degrees of percussion type tones, similar to the tonal envelopes of the piano, guiter, harp, chimes, and any other instrument where the tone starts with an initial pulse. Curve 83 however represents. an envelope containing no percussion, or a staccato envelope. This is common to strings, some Woodwinds, sharp brass, piccolo, etc.

If switch at is moved from contact 85 to contact 86, then condenser '19 will no longer be shortcircuited upon each release of the key H, but will now be put across the terminals of a supply 8'! which has a voltage equal to that of H, and condenser '19 will be charged to 300 volts. It is seen that when key H is pressed now, there is a fully charged condenser across a portion of potentiometer '18, which must discharge thru that portion of the potentiometer before current can start to flow thru bulb l6, and the associated harmonic bulbs. This means that a the voltage across condenser 79 decays after the key is depressed, then cur-rent will slowly and gradually reach the steady state value. determined by the value of resistance 18. At the time'that the steady state value is reached, the voltage ceases: to drop across condenser 19, for it has again reached an equilibrium. The slowness with which the current rises when. the key is depressed: is seen to be again dependent upon the position of slider arm 8|. When the condenser 14 19 is acrossv most of the potentiometer, the effect is greatest, and vice versa.

In Fig. 10a, curves 88 represent the effect. just described. The varying degrees of diminishing effects possible are shown. As with the percussion effect, the minimum diminishing effect obtainable when condenser 19 is across the least portion of potentiometer 18, is the staccato curve of 83. The diminishing effects make it possible for the instrument to imitate the intensity qualities of such instruments as the french horn, saxophone, cathedral toned organ, mellow brass and. most other instruments with the diminishing tone characteristics.

Fairly good results may be obtained with a value of condenser 79 of about five to ten mf. The resistance of potentiometer 18, which is a current limiting resistor as Well as the currentintensifying-envelope regulator, should have. a value of about 200,000 ohms. With switch 84 and potentiometer 78, any desired type of tone start may be had by the proper setting, and switch 84 and potentiometer 18 corresponding to I and J which were listed in the previously described list of controls. Each of the 85 bulb circuits contains one switch M, but they may all be of a multiple switch system controlled from one knob at the panel. All the bulb. 85 circuits also contains one of potentiometer 18, all of which may be simultaneously controlled from one knob as previously described in connection with Fig. 6.

When switch 89 is moved to touch contact 9!, then condenser 92 is put across pole 3 and contact T1. of the key. This means, that every time the key is depressed, condenser is kept discharged, and when the key is opened, it will prevent the voltage across the key from reaching a maximum too rapidly, thereby preventing the bulb from dying out too rapidly when the key is opened. This therefore presents a method for obtaining a soft or diminished ending to the tone intensity. When the switch 89 is moved to contact 93 a more pronounced diminished ending is. possible because a larger condenser 94 is now across the switch. Thus three degrees of tone endings are possible, staccato ending, soft ending and very soft ending. The staccato ending is obtained when switch 89 is across none of the condensers, as is shown in the diagram. Resistor 95 has that same value and function as resistor Bil, described previously.

The curves of Fig. show the effects just described, which take place when the key H is released. Curves 95, 97! and 98 represent respectively the very soft, soft and staccato endings, to any types of tones. Curves 95, 9! and 98- show the endings, however, to sustained type tones, but the instrument, as will be seen later, is also capable of producing gradually diminishing tonal intensities. When these tones end, they too will have a diminished ending due to condensers 92 and 94, regardless of how low the final intensity is. These corresponding endings are shown at 96, 9'! and 98.

Condensers SI and 93 will exhibit good results if they are about 2 ml. each. Switch 89 is one of a multiple switch system, which corresponds to control described previously in the list of controls.

If switch 93 is moved to touch contact l lil, then a closed circuit will never really exist between bulbs IE, supply !'I, resistor 78, and the key. If the key is depressed, and condenser ml: is. initially uncharged, it may be assumed that I will actas a variable resistor whose resistance will vary logarithmically with time from zero to infinity. Thus when the key is depressed, bulb I6 will display any of the starting characteristics described before, and after said characteristics are over, the steady state value of the current will diminish logarithmically to Zero, and the intensity of bulb I6 will behave similarly. As this happens, condenser IOI builds upa voltage across it, which when the current reaches its final value of zero, will be almost equal to the voltage of supply II. These current characteristics should be contrasted to the previous characteristics in which the current sustained itself with no decrease in value thruout theentire time which the key was depressed. Thus two types of notes in general are possible, that type which sustains itself, and that type which diminishes from a certain average starting value, down to zero. In order to make the instrument operable, it is necessary to have condenser IOI completely discharged at the beginning of each key depression. This is accomplished by relay I02 controlling switch I03. At the instant that key II is depressed, relay magnet I 02. is placed in series with condenser I04 across supply 8I. This means that relay magnet I02 will receive current for only a short duration of the time after key II is depressed, during this duration, switch I03 will close and condenser II" will discharge any previous charges thru resistor I which has the same value and function as previously described resistor 80 and contact 11. It is advisable that switch I 03 short-circuit condenser IOI for the complete duration of the starting characteristics as caused by condenser I9. The maximum duration of this may be somewhat less than one second. For this reason, a value of condenser IIM should be chosen, so that with the resistance present in relay magnet I02, current should flow for about one second thru the coil of magnet I02, after depression of key II. It is advisable that switch I03 should open with no delay when key II is released. This is accomplished as seen by having condenser I04 short circuited thru. contact I5 and pole I3, and resistor I00, when key II is released. Resistor I00 has the same value and function as previously described resistor 80. If condensor IOI has a value of about 20 to 30 mfds., then the notes will have a rate of damping equal approximately to that of a conventional piano. Another rate of damping is provided by moving switch 90 from contact I00 to contact I01 which puts condenser I08 into the position formerly occupied by condenser IOI. If condenser I 00 has'a value of from 3 to 4 mf., then a pleasingly short duration may be had which corresponds to that of the chimes, guitar or any short tone-duration instrument. Each of the bulb circuits contains a switch 99, condensers IM and I08, relay I02, condenser I04, resistors I05 and I06. .The switches 99 are of a multiple switch system all controlled at the panel, and they correspond to control K described previously in the list of controls.

-' "The three tonal envelopes just discussed are shown graphically in Fig. 101). These graphs represent the tonal intensities which occur when the key is held down, after any of the previous starts have been effected. Curve I09 shows the sustained tone obtained by switch 99 touching contact IIO, curve III is obtained by switch. 99

touching contact I00, and curve H2 is obtained by switch 99 touching contact I01.

The operation of the sustaining pedal will now be discussed. When switches H3 touch contacts IIQ, condenser H5 will be across supply 81 which has approximately the same voltage as supply IT. This means that condenser II5 will assume the voltageof supply I'l. When the key II is undepressed, there is a voltage across pole I3 and contact I? also nearly equal to the voltage of supply IT, or of condensers II5. If pole of switch II3 were moved from contact II I to contact IIS, then condenser II5 would be across an open key. If however, the polarities of the power supplies were observed as the diagram shows, nothing would happen as the movement of switch II3 would only be serving to connect points of equal potential. If, however, the key N is depressed and released, then condenser II5 will have been discharged thru resistor III (which has the same value and function as resistor and lost its charge. There is now an uncharged condenser across an open key, and current will continue to flow thru the condenser, continuing to light the bulbs which were previously lit by the key depression. The bulbs will stay lit until either condenser H5 has regained all of its charge, or until switch H3 is moved back to contact HQ. The sustaining condenser I I5 operates similarly to the diminishing condensers 92 and 90, but because of its larger capacity, has a more predominant efiect. It is seen that these sustaining condensers produce an effect analogous to the lifting of the dampers in a conventional piano.

The intensity envelope curve which is caused by the sustaining condenser would be similar to curve I I I of Fig. 101). The instant the key is released while the sustaining condenser is across the key terminals, the bulb current begins to diminish logarithmically starting at the exact value the current had just before the key was released, and ending at zero. Each of the circuits has one of condensers H5, resistors II'I, but switch H3 is one of a multiple switch system, one for each key, all of which are controlled from one relay magnet I I8, which is actuated by stepping'on sustaining pedal, II 9.

Due to the fact that most condensers leak current thru their elements, during any length time thatkey II is underpressed, this leakage current can result in a potential buildup across bulb I0, whichwill periodically flash the lamp.However, if the lamp is shunted with a high resistance I20, it will serve to bypass leakage currents, and keep the lamp permanently unlit while the key is underpressed for any length of time.

It is seen from Fig. 10, that there are three distinctly different types of tone-starts; percussive, soft and staccato, two types of tone-durations; sustained and diminishing, and two types of endings; staccato and diminishing. This makes 12 difierent tonal intensity combinations all together, excluding the efiect of the pedal, and the fact there are possible an infinite number of variations within these general types. These combinations represent nearly all the tonal types which would be required of the instrument in imitating the tonal quality and intensity shape of any other instrument.

In previous discussion, bulb intensity envelopes were spoken of and were used to mean tone in"- tensity at the same time. As the tones intensity is at all times proportional to the intensity with which the bulb shines thru the scanner disc 17' into the photoelectric cell, tone intensity and bulb intensity, as well as current intensity may all be considered synonornously, as they would all be representedgraphically by proportional curves. Also, the intensity envelopes were generally considered in connection with the fundamental bulbs, but on examination of the wiring of Fig. 3 and Fig. 9, it is seen that any of the intensity ens velopes made by the circuit of Fig. 9 would affect.

also all of the harmonic bulbs as well as the fundamental of the note under consideration. That is to say, the intensity envelopes of all the notes, fundamentals and harmonics, will all be proportionate or similar, however the proportionality constant of the harmonic bulbs is varied by the harmonic resistors of Fig. 3.

An important advantage of the system as presented, should be noted now. This is in connection with the construction of thev keys of the keyboard. Most other satisfactory working systerns generally require keys which control several more circuits, or have several more individual switches which are closed by one key, than the highest harmonic or partial of which theinstrument is capable. The contacts of these switches generally have to be of expensive metals to insure continual negligible contact resistance and to guard against key noises from getting into the amplifier.

lhe construction costs of the keyboard needed for-my machine are made pratcically n gligible in comparison. Each key handles only one double-throw double-pole switch, the contacts of which do not necessarily have to maintain a low resistance over a long period of time, because all of the circuits contain atleast 200,000 ohms of resistance in them already, and the addition of several more ohms of contact resistance will not matter too seriously.

Key noises previous systems are due to microscopic chips of metal between the key contacts which prevent an instantaneous closing of the circuit. The fact that the chips start conducting in a random manner just before the key is closed results in an amplification of those random currents, or noise in the amplifier due to the key. In the circuits of this invention, it is seen that the key circuits are electrically isolated from the amplifier circuit, and the only possible way for key noises to be amplified is for the key to produce the same random variations in the intensity of the illumination coming from the neon bulb source. There are two factors in the device which prevent this from occurring. (1) The resistance across the terminals of the key, just before actual contact is made during depression, which is the very moment at which keying noises are being formed, is so high that enough potential is not across the bulb to permit it to light, and transmit the key noises. (2) There will generally be enough capacitance in the bulb circuits to prevent any incremental random key currents from producing any variation from the steady, gradual intensity envelope which the bulb would normally follow.

While I have shown what I believe to be the best embodiment of my invention, I do not wish, however, to be confined to the embodiment shown, but what I desire to cover by Letters Patent is set forth in the appended claims.

I claim:

1. In a device for electrically producing a plurality of musical notes arranged in a plurality of octaves, a keyboard comprising a key for each note, a source of direct current energy, a light source controlled by eachkey and arranged to be energized from the direct current source, a plurality of revolving circular perforated areas of the same shape arranged periodically to interrupt the light from each source accordance with the frequency of each note to be produced, a plurality of adjustable circuit means arranged to cause a plurality of light sources of higher octaves to be energized simultaneously with each light source in desired degree under common control with each controlling key, a plurality of rectifier means arranged to block undesired current paths among the adjustable circuit means, photoelectric means responsive to the interrupted light amplifying and reproducing means operatively associated with the photoelectric means arranged to produce the note in audible form.

2. .A device as in claim 1 further comprising adjustable clan =ing control means associated with each key and arranged to modify the rate of use of each light source to control by its d means common to all of the 5 controls for the several keys simultaneously ar into like degrees of modification of response.

3. A device 2 claim 1 L-hGI comprising vimeans cc ed to vary periodically the anvelocity or the revolving perforated areas. 4. In an electrical musical device, a plurality of areas having perforations moving at substantially constant speed, said perforations having the same shape, uniformly spaced light modifying means in each area the spacing being in accordance with the fundamental frequency of a musical note in one of the areas and a harmonic frequency thereof in another of the areas, individual light sources for the fundamental and the harmonic disposed in proximity to the respective areas, photoelectric means responsive to the light from the sources modified by the action of the moving areas, manually operable key means arranged to control the energization of the light source for the fundamental, adjustable timbre control means arranged to control the relative intensity of energization of the light source for the harmonic upon energization of the light source for the fundamental, sustaining means interposed between the manually operable key means and the light sources and arranged to prolong the energization of the light sources beyond the interval determined by actuation of the key means, and amplifying and reproducing means operatively associated with the photoelectric -.means arranged to produce the note in audible form.

5. In an electrical musical device, a plurality of areas having perforations moving at substantially constant speed, said perforations having the same shape, uniformly spaced light modifying means in each area, the spacing being in accordance with the fundamental frequency of musical note in one of the areas and a harmonic frequency thereof in another of the areas, individual light sources for the fundamental and the harmonic disposed in proximity to the respective areas, photoelectric means responsive to the light from the sources modified by the action of the moving areas, manually operable key means arranged to control the energization of the light source for the fundamental, adjustable timbre control means arranged to control the relative intensity of energization of the light source for the harmonic upon energization of the light source for the fundamental, speed varying means operatively associated with moving areas and a low frequency generator disposed to control the effectiveness of the speed varying means periodically and in adjustable degree, and amplifying and reproducing means operatively associated with the photoelectric means arranged to produce the note in audible form.

6. In an electrical musical device, a disc having a multiplicity of similarly shaped perforations, said disc rotating at substantially constant speed and having a first circular light modifying area concentrically disposed with respect to the axis of rotation of the disc, a second light modifying area circular in shape and likewise rotating at substantially constant speed, a plurality of uniformly spaced light modifying means in each area, the spacing in the first area being in accordance with the fundamental frequency of a musical note to be produced by the device and the spacing in the second area being in accordance with a harmonic frequency thereof, individual light sources arranged to illuminate the two areas separately, photoelectric means responsive to the intensity of illumination of the areas as modified by the action of the modifying means, manually operable key means arranged to control the energization of the light source for the fundamental, adjustable timbre control means arranged to control the relative intensity of energization of the light source for the harmonic upon energization of the light source for the fundamental, delay means interposed between the manually operable key means and the light sources and arranged to modify the rate of response of light sources to the key means, and amplifying and reproducing means operatively associated with the photoelectric means arranged to produce the note in audible form.

7. In an electrical musical device, a disc having a multiplicity of similarly shaped perforations, said disc rotating at substantially constant speed and having a first circular light modifying area concentrically disposed with respect to the axis of rotation of the disc, a second light modifying area circular in shape and likewise rotating at substantially constant speed, a plurality of uniformly spaced light modifying means in each area, the spacing in the first area being in accordance with the fundamental frequency of a musical note to be produced by the device and the spacing in the second area being in accordance with a harmonic frequency thereof, individual light sources arranged toilluminate the two areas separately, photoelectric means responsive to the intensity of illumination of the areas as modified by the action of the modifying means, manually operable key means arranged to control the energization of the light source for the fundamental, adjustable timbre control means arranged to control the relative intensity of energization of the light source for the harmonic upon energization of the light source for the fundamental, sustaining means interposed between the manually operable key means and the light sources and arranged to prolong the energization of the light sources beyond the interval determined by actuation of the key means, and amplifying and reproducing means operatively associated with the photoelectric means arranged to produce the note in audible form.

8. In an electrical musical device, a disc having a multiplicity of similarly shaped perforations, said disc rotating at substantially constant speed and having a first circular light modifying area concentrically disposed with respect to the axis of rotation of the disc, a second light modifying area circular in shape and likewise rotating at substantially constant speed, a plurality of uniformly spaced light modifying means in each area, the spacing in the first area being in accordance with the fundamental frequency of a musical note to be produced by the device and the spacing in the second area being in accordance with a harmonic frequency thereof, individual light sources arranged to illuminate the two areas separately, photoelectric means responsive to the intensity of illumination of the areas as modified by the action of the modifying means, manually operable key means arranged to control the energization of the light source for the fundamental, adjustable timbre control means arranged to control the relative intensity of energization of the light source for the harmonic upon energization of the light source for the fundamental, speed varying means operatively associated with moving areas and a low frequency generator disposed to control the effectiveness of the speed varying means periodically and in adjustable degree, and amplifying and reproducing means operatively associated with the photoelectric means arranged to produce the note in audible form.

ALEXANDER ROTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,321 Fisher May 25, 1943 1,986,547 Winch Jan. 1, 1935 2,075,802 Davis Apr. 6, 1937 2,169,842 Kannenberg Aug. 15, 1939 

